We hope to deduce the nature of nucleotide changes induced by a variety of mutagens by examining the spectrum of amino acid changes engendered by the mutagen in Drosophila alcohol dehydrogenase. Alcohol dehydrogenase was chosen for this purpose because it is a relatively small protein, is readily purified, and because it makes up almost 2% of the soluble protein in a fly. In addition, a large number of mutants are already available that affect the enzyme and it has been shown that most of these are in the structural gene.